X, A, 4 



Pratt: Petroletim and Residual Bitumens 



257 



the north the dip changes in direction to the north-northeast 

 and continues unchanged to the region of Mount Benao. Thus 

 an anticline is indicated, the axis of which trends west-north- 

 west and lies close to the north of D outcrop. The southern 

 limb of this fold is not persistent, north-northeast dips being 

 again encountered at a distance of 1 kilometer south of the axis. 



The fragments in the breccia are compact, flintlike rocks, 

 which can best be described, perhaps, by likening them to 

 portions of the clay-tuff hardened through impregnation by 

 mineralizing solutions. That the hard rock may, indeed, have 

 originated by some such process is suggested by the presence in 

 the same neighborhood of peculiar concretions of the same flint- 

 like material in the clay-tuff. These concretions, which have 

 been spoken of as tubelike, are hollow, thick-walled, nearly ver- 

 tical cylinders, piercing the strata. The hollow centers of these 

 concretions, also, are filled with bitumen, and vesicles in the 

 concretion walls contain bitumen. Thin sections of specimens 

 of the breccia and of the concretions show small annular casts 

 which might be taken to represent Globigerina. Globigerina 

 is found both in the Canguinsa and in the Vigo, so that the 

 breccia might be portions of either of these formations so far 

 as this evidence is concerned. Photographs of both the breccia 

 domes and the concretions appear in Plate I. 



The following analyses show in part the composition of a 

 fragment from the breccia and of a piece of clay-tuff from the 

 surrounding beds: 



Table II. — Analyses of breccia and of clay-tuff from Canguinsa clay-tuff: 

 outcrop D, Butason River, Villaba, Leyte." 



Constituent. 



Clay-tuff. 



Breccia. 



Silica (SiOe) 



Alumina (AI2O3) 



Ferric oxide (FeaOa) 



Ferrous oxide (FeO) 



Calcium oxide (CaO) 



Magnesium oxide (MgO) . 

 Loss on ignition 



37.98 

 8.93 

 6.24 

 3.77 



17.56 

 3.80 



21.56 



5.73 



5.98 



0.38 



1.96 



28.80 



13.80 



43.22 



Total 



9.84 



99.87 



» Analyses by T. Dar Juan, chemist. Bureau of Science. 



If the breccia rocks have been formed by the action of solu- 

 tions on clay-tuff, the change has consisted principally in the 

 addition of magnesium and calcium carbonates (especially mag- 

 nesium carbonate) and the subtraction of silica. These results 

 could be accomplished apparently by an alkaline solution, but 

 it is not clear how the decrease in ferric iron could have been 



